Right: after the Port Arthur massacre, the Australian federal government acted to ensure that weapons used in the shootings would not be as readily available. To this end, a national "buyback" of guns was legislated and weapons ranging from .22 rimfires to military-style rifles were compulsorily acquired and destroyed.

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Gun laws have only become a notable issue in Australia since the 1980s. Low levels of violent crime through much of the 20th century kept levels of public concern about firearms low. However, in the last two decades of the century, following several high profile multiple murders and a media campaign, the Australian government co-ordinated more restrictive firearms legislation with all state governments. Australia today has arguably some of the most restrictive firearms legislation in the world.
From 1984 to 1996, multiple killings aroused public concern. The 1984 Milperra massacre was a major incident in a series of conflicts between various 'outlaw motorcycle gangs'. In 1987, the Hoddle Street massacre and the Queen Street massacre took place in Melbourne. In response, several states required the registration of all guns, and restricted the availability of self-loading rifles and shotguns. In the Strathfield massacre in New South Wales, in1991, two were killed with a knife, and five more with a firearm. Tasmania passed a law in 1991 for firearm purchasers to obtain a licence, though enforcement was light. Firearm laws in Tasmania and Queensland remained relatively relaxed for long arms. In 1995, Tasmania had the second lowest rate of homicides per head of population.
Shooting massacres in Australia and other English-speaking countries often occurred close together in time. Forensic psychiatrists attribute this to copycat behaviour, which is in many cases triggered by sensational media treatment. Mass murderers study media reports and imitate the actions and equipment that are sensationalised in them.

The Port Arthur massacre and its consequences
The Port Arthur massacre, in 1996, transformed gun control legislation in Australia. Thirty five people were killed and 21 wounded when a man with a history of violent and erratic behaviour beginning in early childhood opened fire on shop owners and tourists with two military style semi-automatic rifles. Six weeks after the Dunblane massacre in Scotland, this mass killing at the notorious former convict prison at Port Arthur horrified the Australian public and had powerful political consequences.
The Port Arthur perpetrator, Martin Bryant, said he bought his firearms from a gun dealer without holding the required firearms licence.
Prime Minister John Howard, then newly elected, immediately took the gun law proposals developed from the report of the 1988 National Committee on Violence and forced the states to adopt them under a National Firearms Agreement. This was necessary because the Australian Constitution does not give the Commonwealth power to enact gun laws. The proposals included a ban on all semi-automatic rifles and all semi-automatic and pump-action shotguns, and a tightly restrictive system of licensing and ownership controls.

Some discussion of measures to allow owners to undertake modifications to reduce the capacity of magazine-fed shotguns ("crimping") occurred, but the government refused to permit this.
Surveys showed up to 85% of Australians supported gun control, but some farmers and sporting shooters strongly opposed the new laws.
The government planned a series of public meetings to explain the proposed changes. In the first meeting, on the advice of his security team, Howard wore a bullet-resistant vest, which was visible under his jacket. Many shooters were critical of this.
Some shooters applied to join the Liberal Party of Australia in an attempt to influence the government, but the Liberal Party barred them from membership. A court action by 500 shooters seeking admission to membership eventually failed in the Supreme Court of South Australia.
Because the Australian Constitution prevents the taking of property without just compensation the federal government introduced the Medicare Levy Amendment Act 1996 to raise the predicted cost of A$500 million through a one-off increase in the Medicare levy. The gun buy-back scheme started on 1 October 1996 and concluded on 30 September 1997. The buyback purchased and destroyed more than 631,000 firearms, mostly semi-auto .22 rimfires, semi-automatic shotguns and pump-action shotguns. Only Victoria provided a breakdown of types destroyed, and in that state less than 3% were military style semi-automatic rifles.

Current Australian firearm laws
State laws govern the possession and use of firearms in Australia. These laws were largely aligned under the 1996 National Agreement on Firearms. Anyone wishing to possess or use a firearm must have a Firearms Licence and, with some exceptions, be over the age of 18. Owners must have secure storage for their firearms.
Before someone can buy a firearm, he or she must obtain a Permit To Acquire. The first permit has a mandatory 28-day delay before it is first issued. In some states (e.g., Queensland, Victoria, and New South Wales), this is waived for second and subsequent firearms of the same class. For each firearm a "Genuine Reason" must be given, relating to pest control, hunting, target shooting, or collecting. Self-defence is not accepted as a reason for issuing a license, even though it may be legal under certain circumstances to use a legally held firearm for self-defence.
Each firearm in Australia must be registered to the owner by serial number. Some states allow an owner to store or borrow another person's registered firearm of the same category.

Firearms categories
Firearms in Australia are grouped into categories determined by the National Firearm Agreement with different levels of control. The categories are:

Category A: Rimfire rifles (not semi-automatic), shotguns (not pump-action or semi-automatic), air rifles, and paintball markers. A "Genuine Reason" must be provided for a Category A firearm.

Category B: Centrefire rifles (not semi-automatic), muzzleloading firearms made after 1 January 1901. Apart from a "Genuine Reason", a "Genuine Need" must be demonstrated, including why a Category A firearm would not be suitable.

Category D: Semi-automatic centrefire rifles, pump-action or semi-automatic shotguns holding more than 5 rounds. Functional Category D firearms are restricted to government agencies and a few occupational shooters. Collectors may own deactivated Category D firearms.

Category H: Handguns including air pistols and deactivated handguns. (Albeit both SA and WA do not require deactivated handguns to be regarded as handguns after the deactivation process has taken place. This situation was the catalyst in QLD for the deactivation and diversion of thousands of handguns to the black-market - the loophole shut since 2001) This class is available to target shooters. To be eligible for a Category H firearm, a target shooter must serve a probationary period of six months using club handguns, and a minimum number of matches yearly to retain each category of handgun.

These categories - A,B,C,D and H, were those determined by the NFA. The others listed here are determined by the states that have implemented them at their own discretion.
Target shooters are limited to handguns of .38 or 9mm calibre or less and magazines may hold a maximum of 10 rounds. Participants in certain "approved" pistol competitions may acquire handguns up to .45", currently Single Action Shooting and Metallic Silhouette. IPSC shooting is approved for 9mm/.38/.357 handguns that meet the IPSC rules, but larger calibres are not approved for IPSC handgun shooting contests. Category H barrels must be at least 100mm (3.94") long for revolvers, and 120mm (4.72") for semi-automatic pistols unless the pistols are clearly ISSF target pistols: magazines are restricted to 10 rounds. Handguns held as part of a collection were exempted from these limits.

Category R/E: Restricted weapons: machine guns, rocket launchers, assault rifles, flame-throwers, anti-tank guns, Howitzers, artillery, etc. can be owned by collectors in some states provided that these weapons have been rendered permanently inoperable. They are subject to the same storage and licensing requirements as fully functioning firearms.
Certain Antique firearms can in some states be legally held without licences. In other states they are subject to the same requirements as modern firearms.
All single-shot muzzle-loading firearms manufactured before 1 January 1901 are considered antique firearms. Four states require licences for antique percussion revolvers and cartridge repeating firearms, but in Queensland and Victoria a person may possess such a firearm without a licence, so long as the firearm is registered (percussion revolvers require a license in Victoria).

Australia has very tight restrictions on items which are far less controlled in comparable societies such as the UK. Air pistols, elsewhere unrestricted, are as difficult to get as centrefire and rimfire handguns, and low-powered airguns are as difficult as cartridge arms to license. Airsoft guns are banned in all states and non-firing replicas banned in most. Suppressors (or 'silencers') which are legal in the UK and New Zealand, are extremely restricted in Australia to a few government bodies.